This invention concerns, generally, a system for measuring the spatial distribution of charged particle emitting radionuclides across the surface of a material and, more particularly, a process for precision measurement of charged particle emissions from a surface and an apparatus for providing a high resolution digital image of the distribution of such emissions in a minimum exposure time over a relatively large surface area.
There are several procedures in which it is necessary to measure detailed distributions of charged particle emitting radionuclides across the surface of a material. Some of these involve relatively large surface areas, up to 1/4 square meter. One such procedure is mapping concentrations of phosphorus-32 labelled compounds in thin layer polyacrylamide gels. In the past, several different approaches to this measurement problem have been employed.
Autoradiography provides simultaneous, high resolution recording for a large area. However, photographic film is relatively insensitive to energetic beta emissions, has limited exposure range, must be developed and read by additional procedures, and records a background from chemical film fog and natural sources of radioactivity. Intensifying screens are used to enhance the sensitivity of photographic film, but they degrade spatial resolution.
Another approach uses scanning detectors of a variety of types, including gas ionization detectors, scintillators, and other solid state detectors. Some of these detect only a point at a time, while others simultaneously record a line or a small area. However, scanning detectors require a relatively long time to cover an area that is large compared to the sensitive area of the detector.
Segmented detectors have also been constructed, using multiples of the type of detectors employed in scanning. Both scanning and segmentation may introduce boundary effects, mechanical distortion, and artifacts in their measured distributions.
Still another approach has been large area detectors. However, high resolution solid state devices, such as multichannel plates, have proven difficult to construct in large sizes. Existing techniques involving gas ionization detectors have not been capable of providing high spatial resolution, particularly for energetic beta emissions.
It is therefore a primary objective of the present invention to provide an apparatus and a process for direct digital measurement of surface distributions of charged particle emitting radionuclides, capable of high spatial precision, resolving spots of radionuclide concentrations at very small separations.
It is another objective of the present invention to provide measurement of radionuclide distributions over large surface areas with high efficiency in detecting radioactive emissions and consequent short exposure time.
It is still another objective of the present invention to provide high resolution, large area measurements of radionuclides with energetic beta emissions, such as phosphorus-32.
It is a further objective of this invention to provide quantitative measurements of radionuclide activity with wide dynamic range, permitting the measurement of low radionuclide activity concentrations in the presence of high activity concentrations.